Currently, as a gas used as a semiconductor material, a gas in which a volume concentration of impurities is at a ppt-ppb level is preferred to a gas in which a volume concentration of impurities is at a ppb-ppm level.
Examples of a gas used as a semiconductor material include a hydride gas such as ammonia, silane, or phosphine; a halide gas such as hydrogen fluoride, hydrogen chloride, or hydrogen bromide; and a halogen gas such as fluorine, chlorine, or bromine. These gases have high reactivity and strong corrosivity.
An example of a gas purification technique is a purification method using a gas separation membrane. Examples of the purification using a gas separation membrane include the purification of hydrogen, helium, or argon, in which a volume concentration of impurities is at a % level, using a polyaramid membrane, etc. (see patent document 1); the purification of phosphine, in which a volume concentration of impurities is at a % level, using a polyaramid membrane, etc. (see patent document 2); the purification of carbonyl fluoride, in which a volume concentration of impurities is at a % level, using a polyimide membrane (see patent document 3); the recovery of ammonia using a pervaporation membrane (see patent document 4); the purification of tetrafluoroethylene, in which a volume concentration of impurities is at a % level, using a polyimide membrane, etc. (see patent document 5); the purification of silane, in which a volume concentration of impurities is at a % level, using a membrane made by sulfonated polysulfone (see patent document 6); and the purification of chlorine using an inorganic porous membrane of silica and alumina, etc. (see patent document 7).
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. Hei 7-171330
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. 2002-308608
[Patent Document 3]
Japanese Unexamined Patent Application, First Publication No. 2005-154203
[Patent Document 4]
Japanese Unexamined Patent Application, First Publication No. 2005-60225
[Patent Document 5]
Japanese Unexamined Patent Application, First Publication No. 2003-37104
[Patent Document 6]
Japanese Patent Publication No. 2615265
[Patent Document 7]
Japanese Patent Publication No. 3433226